Rijndael decryption in WinRT

我正在尝试编写一个解密字节数组的方法。

• 键是固定的和24字节长

当我做数据的实际解密时，我得到一个异常The supplied user buffer is not valid for the requested operation，我希望有人能帮助我!

        // Get the key and put into IBuffers
        IBuffer keyBuffer = CryptographicBuffer.CreateFromByteArray(cKey);
        IBuffer plainText = CryptographicBuffer.CreateFromByteArray(cData);
        byte[] decryptedData;
        // Setup an AES key, using AES in CBC mode and applying PKCS#7 padding on the input
        SymmetricKeyAlgorithmProvider aesProvider = SymmetricKeyAlgorithmProvider.OpenAlgorithm(SymmetricAlgorithmNames.AesEcbPkcs7);
        CryptographicKey aesKeySymm = aesProvider.CreateSymmetricKey(keyBuffer);

        // Decrypt the data and convert it to byte array
        // EXCEPTION ON THIS LINE: "The supplied user buffer is not valid for the requested operation."
        IBuffer decrypted = CryptographicEngine.Decrypt(aesKeySymm, plainText, null);
        CryptographicBuffer.CopyToByteArray(decrypted, out decryptedData);
        return decryptedData;